It is common in the manufacture of sign posts and the like to provide one or more series of regularly spaced mounting apertures along the length of the post. This permits convenient field installation of the sign on the post after the post has been set. It thus avoids the need for drilling apertures in the field and even removes the need for the installer to decide at what point along the post the sign is to be mounted, until after the post is set.
When such posts are manufactured by a continuous rolling mill, the apertures must be provided as an additional manufacturing step performed either before or after the tube formation process. In the typical continuous rolling process for forming tubing without apertures, flat stock is transversely bent until the lateral ends are brought into abutment and welded together to form a tube. The formed tube is then subjected to alkali wash, water rinse and pickling steps to remove dirt, grease and other contaminants prior to drying in preparation for galvanization of the outside surface of the tube by passing the tube through a molten zinc bath. The flat stock cannot be provided with the apertures prior to tube formation and still retain the galvanization step after tube formation because the wash, rinse and pickling liquids would have access to the inside of the formed tube where they could not be effectively removed prior to galvanizing. The entrance of such cleansing liquids into the molten zinc bath could have catastrophic consequences. Not only would the zinc bath be contaminated, but water and molten zinc are an explosive combination. Thus the flat stock is either galvanized prior to punching the apertures and the tube formation process occurring without the typical galvanization step; or the tube is formed in the above-described typical manner with the apertures formed in the tube off-line as a last manufacturing step.
It is common that no additional corrosion protection is applied after the series of mounting holes is drilled in a length of pipe. Thus, the material defining these apertures is bare metal and has no protective coating. The aperture used to mount the sign is somewhat shielded from the elements by the presence of the sign and the mounting fastener. However, the remaining apertures, available but unused, represent easy targets for the onset of rust. Rust not only makes the post unsightly, but is progressively weakens the post until the point where the post is structurally insufficient and must be replaced. Rusting continues under normal environmental conditions and under extreme conditions, such as the splashing of salt water on the posts by passing vehicles, the rusting process is greatly accelerated.
Apart from the oxidation problem, the provision of a series or multiple series of apertures in the post also results in a significant reduction of the load-carrying ability of the post. This is particularly true when the post is used as a horizontally disposed, load-carrying member. With the use of so many holes, thicker gauge stock is required to obtain a given load rating.
A sign post has been proposed including a number of mounting apertures so completely filled by knockouts as to render the wall forming the post impervious to liquids. Each knockout is connected to the surrounding material defining the aperture by a number of tabs. While this post works well for its intended purpose, removal of a knockout by application of a sharp blow can cause the material forming the tabs to extend inside the post where it can interfere with telescopic reception of a close-fitting extension post by the sign post. For further information regarding the structure and operation of such a sign post, reference may be made to commonly assigned U.S. Pat. No. 4,611,480, the teachings of which are hereby incorporated by reference.